1. Field of the Invention
This invention relates generally to disk apparatuses and, more particularly, to a disk apparatus for setting to a counter a count value corresponding to the number of tracks to jump over, subtracting the count value each time a rising or trailing edge is detected in the zero-cross signal, and applying brake to finish jump when the count value reaches 0.
2. Description of the Prior Art
In the conventional disk apparatus of this kind, when seek is instructed, a count value is set to a counter correspondingly to the number of tracks to jump over. When the optical pickup is moved in a radial direction of the disk, counting is made on rising and trailing edges of a zero-cross (TZC) signal switching between high and low levels at zero-cross points of a tracking error (TE) signal. If the remaining count value reaches 1, a brake pulse is outputted to decelerate the optical pickup and turn on tracking servo. In this manner, the optical pickup is jumped from a track including a current position over to a desired track, thus seeking a target position.
Meanwhile, where using an ASMO (Advanced-Storage Magnet-Optical) disk capable of land/groove-recording, the output polarity to a tracking actuator for tracking on is different in polarity between land and groove. That is, as shown in FIG. 8, for tracking on a groove, the tracking error signal is same in polarity as the output to the tracking actuator. However, where a land is to be tracked on, the polarity is reversed. Incidentally, in FIG. 8, the output to the tracking actuator is illustrated in parallel with the horizontal axis, wherein the polarity of the output to the tracking actuator is taken positive in a direction toward an outer periphery of the disk and negative in a direction toward an inner periphery thereof. Consequently, it is a conventional practice to differ the polarity in the output to the tracking actuator depending upon a land or a groove to be tracked on.
However, if the TZC signal in its offset value varies during seek, disturbance possibly occurs in the TZC signal, resulting in incorrect counting of TZC signal edges. For example, where jumping to a land, if a TZC signal edge is miscounted, tracking on would be toward a groove. That is, the output to the tracking actuator is made reverse in polarity upon effecting tracking. This might unsuccessfully introduce a track, leading to overrun of the optical pickup, i.e. unstable seek.